1,531 research outputs found
Measurements of the Cross Section for e+e- -> hadrons at Center-of-Mass Energies from 2 to 5 GeV
We report values of for 85 center-of-mass energies between
2 and 5 GeV measured with the upgraded Beijing Spectrometer at the Beijing
Electron-Positron Collider.Comment: 5 pages, 3 figure
First Measurement of the Branching Fraction of the Decay psi(2S) --> tau tau
The branching fraction of the psi(2S) decay into tau pair has been measured
for the first time using the BES detector at the Beijing Electron-Positron
Collider. The result is ,
where the first error is statistical and the second is systematic. This value,
along with those for the branching fractions into e+e- and mu+mu of this
resonance, satisfy well the relation predicted by the sequential lepton
hypothesis. Combining all these values with the leptonic width of the resonance
the total width of the psi(2S) is determined to be keV.Comment: 9 pages, 2 figure
Measurement of decays to baryon pairs
A sample of 3.95M decays registered in the BES detector are used
to study final states containing pairs of octet and decuplet baryons. We report
branching fractions for , ,
, ,
, ,
, and . These results
are compared to expectations based on the SU(3)-flavor symmetry, factorization,
and perturbative QCD.Comment: 22 pages, 21 figures, 4 table
A Unified Approach to the Classical Statistical Analysis of Small Signals
We give a classical confidence belt construction which unifies the treatment
of upper confidence limits for null results and two-sided confidence intervals
for non-null results. The unified treatment solves a problem (apparently not
previously recognized) that the choice of upper limit or two-sided intervals
leads to intervals which are not confidence intervals if the choice is based on
the data. We apply the construction to two related problems which have recently
been a battle-ground between classical and Bayesian statistics: Poisson
processes with background, and Gaussian errors with a bounded physical region.
In contrast with the usual classical construction for upper limits, our
construction avoids unphysical confidence intervals. In contrast with some
popular Bayesian intervals, our intervals eliminate conservatism (frequentist
coverage greater than the stated confidence) in the Gaussian case and reduce it
to a level dictated by discreteness in the Poisson case. We generalize the
method in order to apply it to analysis of experiments searching for neutrino
oscillations. We show that this technique both gives correct coverage and is
powerful, while other classical techniques that have been used by neutrino
oscillation search experiments fail one or both of these criteria.Comment: 40 pages, 15 figures. Changes 15-Dec-99 to agree more closely with
published version. A few small changes, plus the two substantive changes we
made in proof back in 1998: 1) The definition of "sensitivity" in Sec. V(C).
It was inconsistent with our actual definition in Sec. VI. 2) "Note added in
proof" at end of the Conclusio
Observation of Y(2175) in
The decays of are analyzed using a sample of events collected with the BESII detector at the Beijing
Electron-Positron Collider (BEPC). A structure at around GeV/ with
about significance is observed in the invariant mass
spectrum. A fit with a Breit-Wigner function gives the peak mass and width of
GeV/ and GeV/, respectively, that are consistent with those
of Y(2175), observed by the BABAR collaboration in the initial-state radiation
(ISR) process . The production branching
ratio is determined to be , assuming that the Y(2175) is a state.Comment: 5 pages, 4 figures, accepted by Phys. Rev. Let
Observation of decays into vector meson pairs , , and
Decays of to vector meson pairs , and
are observed for the first time using
\psip events accumulated at the BESIII detector at the BEPCII
collider. The branching fractions are measured to be , , and , for , , and ,
respectively. The observation of decays into a pair of vector
mesons , and indicates that the hadron
helicity selection rule is significantly violated in decays. In
addition, the measurement of gives the rate of doubly
OZI-suppressed decay. Branching fractions for and
decays into other vector meson pairs are also measured with improved precision.Comment: 4 pages, 2 figure
Partial wave analysis of J/psi to p pbar pi0
Using a sample of 58 million events collected with the BESII
detector at the BEPC, more than 100,000 events are
selected, and a detailed partial wave analysis is performed. The branching
fraction is determined to be . A long-sought `missing' , first observed in , is observed in this decay too, with mass and width of
MeV/c and MeV/c,
respectively. Its spin-parity favors . The masses, widths, and
spin-parities of other states are obtained as well.Comment: Add one author nam
First Observation of the Decays chi_{cJ} -> pi^0 pi^0 pi^0 pi^0
We present a study of the P-wave spin -triplet charmonium chi_{cJ} decays
(J=0,1,2) into pi^0 pi^0 pi^0 pi^0. The analysis is based on 106 million
\psiprime decays recorded with the BESIII detector at the BEPCII electron
positron collider. The decay into the pi^0 pi^0 pi^0 pi^0 hadronic final state
is observed for the first time. We measure the branching fractions B(chi_{c0}
-> pi^0 pi^0 pi^0 pi^0)=(3.34 +- 0.06 +- 0.44)*10^{-3}, B(chi_{c1} -> pi^0 pi^0
pi^0 pi^0)=(0.57 +- 0.03 +- 0.08)*10^{-3}, and B(chi_{c2} -> pi^0 pi^0 pi^0
pi^0)=(1.21 +- 0.05 +- 0.16)*10^{-3}, where the uncertainties are statistical
and systematical, respectively.Comment: 7 pages, 3 figure
Study of and
The decays and have been
investigated with a sample of 225.2 million events collected with the
BESIII detector at the BEPCII collider. The branching fractions are
determined to be and . Distributions of the angle
between the proton or anti-neutron and the beam direction are well
described by the form , and we find
for and
for . Our branching-fraction
results suggest a large phase angle between the strong and electromagnetic
amplitudes describing the decay.Comment: 16 pages, 13 figures, the 2nd version, submitted to PR
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